Non-polymer catechins are reported to have a suppressing effect on the increase of cholesterol and the like (see, for example, Patent Document 1). For such a physiological effect to materialize, it is necessary for an adult to drink 4 to 5 cups of tea per day. Therefore, there has been a need for the development of a technology making it possible for a beverage to contain non-polymer catechins at a high concentration so that a large amount of catechins can be ingested with ease.
The methods that enable non-polymer catechins to be contained at a high concentration in a green tea beverage include an extraction method characterized by extracting a great deal of catechins from green tea leaves. On the other hand, with regards to beverages other than green tea beverages, there is a method characterized by adding non-polymer catechins in a dissolved state to a beverage by making use of a concentrated green-tea extract or the like (see, for example, Patent Document 2).
Nonetheless, these conventional methods aimed at extracting a great deal of catechins from tea leaves have a problem in common, in that the extract tends to accompany the bitterness and acridness inherent to green tea leaves, along with the occurrence of sediment in the extract. Meanwhile, even the methods associated with beverages other than green tea beverages are prone to similar problems even if allowed to make use of a concentrated green-tea extract or its purification product, albeit the level of seriousness regarding the problem differs between them.
In order to improve the taste of green tea leaves, some methods have been proposed, such as a method for producing astringency-eliminated tea by spraying a small amount of a 10 to 20 wt % aqueous solution of ethanol to tea leaves in a production process of crude tea or finished tea (for example, Patent Document 3). However, no consideration has been made as to the suppression of bitterness, acridness or sediment in a tea extract, and no disclosure has been made about the control of non-polymer catechins or lipids, either.
For the production of an extract from green tea leaves, on the other hand, a number of methods have been disclosed such as the extraction of tea catechins (for example, Patent Documents 4 to 7), a production method of tea leaf saponin (for example, Patent Document 8), and a production method of a coloring matter-containing dried product. However, these methods are all intended to recover useful component or components from green tea leaves, and are not deemed to be methods for producing useful green tea leaves.
Patent Document 1: JP-A-S60-156614
Patent Document 2: JP-A-S60-13780
Patent Document 3: JP-A-S61-249346
Patent Document 4: JP-A-S60-13780
Patent Document 5: JP-A-S59-219384
Patent Document 6: JP-A-2002-104982
Patent Document 7: JP-A-H09-322710
Patent Document 8: JP-A-H07-61993
Patent Document 9: JP-A-2004-49201